To satisfy a recent request for reducing a fuel cost of automobiles, there is accordingly a demand for the development of conjugated diene polymers having, as a rubber material for tires, low rolling resistance, excellent abrasion resistance and failure characteristics and also excellent drivability typified by wet skid resistance.
A decrease in hysteresis loss of a vulcanized rubber is necessary for reducing the rolling resistance of tires. As evaluation indicators of a vulcanized rubber, rebound resilience at from 50 to 80° C., tan δ at from 50 to 80° C., and heat build-up measured by a Goodrich meter are used. Rubber materials having high rebound resilience at from 50 to 80° C., or low tan δ at from 50 to 80° C. or small Goodrich heat build-up are preferred. Natural rubber, polyisoprene rubber and polybutadiene rubber are known as rubber materials having low hysteresis loss, but they have undesirably low wet skid resistance. As a method of reducing hysteresis loss without damaging wet skid resistance, proposed is a method of introducing a modifying group at the polymer end of styrene-butadiene (co)polymers having various structures, which are obtained by polymerization in a hydrocarbon solvent in the presence of an organolithium initiator.
WO01-23467 discloses a silica composition of a modified polymer available by reacting the active end of a rubbery polymer with a polyfunctional compound having, in the molecule thereof, an epoxy group. This silica composition however does not have sufficiently improved hysteresis loss and abrasion resistance, and in addition, improvement effects on a carbon blend are small.
Japanese Patent Laid-Open No. Hei 11-29659 and Japanese Patent Laid-Open No. Sho 61-296001 disclose a modified polymer obtained by reacting the active end of a rubbery polymer with a specific amide compound, and a blend composition of the polymer. These modified polymers, when mixed with silica or carbon, have improved hysteresis loss and abrasion resistance, but improvement is not satisfactory.
Japanese Patent Laid-Open No. Hei 7-233217 and WO2003-087171 disclose a diene rubber having a tertiary amino group and an alkoxysilyl group introduced therein. Addition of such a modified polymer to a composition containing silica or a mixture of silica and carbon black improves its physical properties to some extent. The silica-containing composition is inferior in processability to the carbon-black-containing composition so that its processing cost is higher. Polymers having, introduced therein, a functional group having affinity with silica are likely to have deteriorated processability in blending so that their use is limited.
Japanese Patent Laid-Open No. 2004-18795 describes a modified polymer having a primary amino group and an alkoxysilyl group. In addition, it discloses a polymer having a polymer chain copolymerized with a polyfunctional monomer or a polymer obtained by coupling at least a portion of a copolymer with a two or higher functional coupling agent. These modified polymers however have problems such as deterioration of processability due to strong affinity with a filler resulting from the primary amino group and cumbersome control of a hydrolysis step to produce the primary amine.
Japanese Patent Laid-Open No. Hei 11-349632 discloses a diene rubber having a methyleneamino group and an alkoxysilyl group introduced therein and a blend composition of the diene rubber. These modified polymers have, in a carbon-black-containing or silica-containing composition, improved hysteresis loss and abrasion resistance, but their balance between hysteresis loss and wet skid resistance is not improved sufficiently.
Japanese Patent Laid-Open No. 2005-290355 discloses a modified polymer having a tertiary amino group and alkoxysilyl group and a blend composition thereof. Use of such a modified polymer for a silica-containing composition improves hysteresis loss, but its improvement is insufficient.
Japanese Patent Laid-Open No. Hei 11-189616 discloses a modified polymer available by reacting the active end of a rubbery polymer with a cyclic aminoalkoxysilane compound, and a blend composition of the modified polymer. These modified polymers are effective, in a carbon-black-containing or silica-containing blend composition, for improving hysteresis loss and abrasion resistance without impairing wet skid resistance, but the blend composition is likely to have inferior processability.
Japanese Patent Laid-Open No. 2004-182894 discloses a modified polymer having a secondary amino group and an alkoxysilyl group obtained by treating an alkoxysilane compound having an amino group containing an active hydrogen with an organometal compound, reacting the resulting compound with the active end at the polymer, and then removing the metal. The treatment with the organometal compound is however not performed uniformly so that a modification amount is not sufficient. Use of the modified polymer for a silica-containing composition improves hysteresis loss, but the improvement is not sufficient.    Patent Document 1: WO01-23467    Patent Document 2: Japanese Patent Laid-Open No. Hei 11-29659    Patent Document 3: Japanese Patent Laid-Open No. Sho 61-296001    Patent Document 4: Japanese Patent Laid-Open No. Hei 7-233217    Patent Document 5: WO2003-087171    Patent Document 6: Japanese Patent Laid-Open No. 2004-18795    Patent Document 7: Japanese Patent Laid-Open No. Hei 11-349632    Patent Document 8: Japanese Patent Laid-Open No. 2005-290355    Patent Document 9: Japanese Patent Laid-Open No. Hei 11-189616    Patent Document 10: Japanese Patent Laid-Open No. 2004-182894